Production of plywood and other joined wooden articles



hatented Nov. 5, 1935 PRODUKJTION F PLYWOOD AND OTHER JOINED WOODEN ARTIQLES Karl Vierling, Matthias Schmihing, and Hugo Klingenherg,

Ludwigshafen on the Rhine,

Germany, assignors to I. G. Farbenindnstrie Aktiengesellschaft, Frankfort on the Main,

Germany No Drawing. Application July 11,1930, Serial No. 467,384. In Germany July 24, 1929 Claims.

of wood is combined with another wooden surface the single wooden layers are usually joined with the aid of adhesives made from common glue or from casein, the process consisting for example in painting one or more single slabs ofveneer with viscous adhesive preparations, combining the coated slabs and subjecting them to high mechanical pressure, if desired while heating. When employing common glue the process is rather tedious due to the long period of time required by the glue for obtaining its maximum of adhesiveness. Preparations from casein can be applied in the form of the so-called cold glues, in contrast to common glue which is usually applied in the form of a hot viscous solution. The employment of cold glues from casein is, however, met with several disadvantages and neutral solutions of condensation products from urea and formaldehyde have been suggested as substitutes for the adhesives from casein. These preparations from the said condensation products are quite satisfactory for combining paper, leather or other soft materials but for the production of plywood and other joined wooden articles these preparations have not proved entirely satisfactory.

,We have now found that plywood and other joined wooden articles with a particularly high strength can be obtained when the single parts,

for example slabs of veneer, are coated with a solution of a water-soluble condensation product of a urea and formaldehydmto which solution a small amount of an acid reacting agent has been added shortly before coating the surfaces to be joined. By the said addition the single parts of wood are firmly joined in a short time on pressing the combined layers in a mechanical press, the quantity of acid reacting agent being -usually from about 0.4 m2 per cent by weight 'of the urea-formaldehyde condensation product.

The said upper limit shouldnot be exceeded sinceotherwise the glue may be rendered too viscous for easily coating the slabs and solidifies too quickly. The said acid reacting agents may be chosen from acids such as hydrochloric, sulphuric, phosphoric, acetic, oxalic, lactic acids, acid reacting salts such as acid sodium sulphate, monoammonium phosphate or aluminium chloride, and agents which split oif acids when incorporated with the mixture, such as ammonium chloride, ammonium sulphate, copper sulphate or copper chloride. In order to improve the uniform dispersion of the glue onto the wood and the desired degree of viscosity, starch, potato flour, ground potato flakes or other pulverized fillers of most diiferent nature may be added. 5

The aforesaid water-soluble condensation, products from urea and formaldehyde may be obtained for example by condensing a urea and formaldehyde in the presence of water and/or of an organic solvent/with the aid of an acid in condensing agent, such as the acid agents mentioned above or the so-called bufier compounds or buffer mixtures as for example monosodium phosphate or a mixture thereof withv di-sodium phosphate, or the urea and formaldehyde may be if first condensed in the presence of a small quantity of alkali whereby methylol derivatives of the urea employed are formed and these methylol compounds, such as monoor di-methylol urea, monoor di-methylolthiourea and the like, may be then further condensed with the aid of acid condensing agents; care being taken, however, that the condensation is not carried so far that water-insoluble products are obtained. When the condensation has been carried out in the pres ence of such quantities of water that the condensation products are obtained in the form of their aqueous solutions of such concentration that they may be directly employed for the purpose of the present invention, no dilution with wate or, on the other hand, evaporation of water will be required, the strength of the. solutions employed for the present process being usually between 20 and 50 per cent of condensation product of the solutions. These solutions usually possess a rather low viscosity, especially those with a low content of condensation products and their viscosity may be easily increased by the beforementioned addition of carbohydrates or flour, which are usually employed in quantities of from 5 to 40 per cent by weight of the solutions and do not impair the adhesive power of the glue. If desired up to 10 per cent of an animal glue such as common bone-glue or casein may be added.

The plywood and other joined wooden articles obtained in the aforesaid manner show a particularly high strength which is higher than that of joining with the aid of glue from a urea-for-- maldehyde condensation product free from acid reacting agent, the joints being moreover highly resistant to water. In any case the single original parts of wood cannot be torn off from each other as such along the joint but the wood breaks. within the fibres.

The following examples will further illustrate 5 how the present process may practice but the invention is not restrictedthere- Example 1 200 kilograms of- 30 per cent. aqueous formaldehyde are incorporated with IOO grams of mono- .sodium phosphate and heated to 95 C. Asolu- 'tion, heated to 70 C., of 60 kilograms of urea in 30 kilograms of water i then introduced into the solution ,of formaldehyde and 150 grams of tri sodium phosphate are added whereupon the mixture is evaporated in vacuo and below C. until it has a content of 35 per cent of condensation product.

1000 parts of the 35 per cent aqueous solution are stirred with 200 'partsof potato starch, where uponlO parts of 2 N-sulphuric acid are added.

"Ihe glue obtained remains in the liquid condition for from. 8 tov 12 hours within which time slabs of beech wood of 1.5 millimetres thickness are coated with the preparation and then the whole is pressed for 5 minutes at 100 C. and at-a pressure of 20 kilograms per square centimetre. When the veneers have been Joined while crossing the a grain the strength of the product is from 25 to 27 kgs. per square centimetre, whereas when the slabs have been joined in parallel direction of the grain a strength of from to kilograms per square centimetre is obtained.

' Example? 1000 parts of an aqueous 45 per cent solution of the condensation product prepared according to Example 1 are incorporated with 10 per cent of wheat flour and 30 parts of 5 per cent aqueous ammonium chloride. Slabs of beech wbod which are coated with the glue and then pressed at 100 step is eifected and are 2 centimetres wide and 0.4 centimetre thick.

' 2,o1o,ss4 be carried out in C. for 8 minutes at a pressure of 20 kilograms per square centimetre. The strength of the finished product is from to 140 kilograms per square centimetre when the slabs have been joined in whereas the strength is from 40 to 50 kilograms per square centimetre only when no ammonium .chloride has-been added. What we claim is':-

1. The process of joining wooden surfaces which 10 comprises applying to said surfaces a solution of a water soluble condensation product of a urea and formaldehyde to which condensation product an acid reacting agent, inert to formaldehyde has been added shortly before the solution applying 15 step is effected and pressing at an elevatedtemperature.

2. The process according to claim 1 in which the pressure is about 20 kilograms per square centimeter and the temperature is about C. 20 3. The process according to claim 1 in which the acid reacting substance is added'in an amount ranging from .4 to 2 per cent of the weight of the I condensation product, 1 1

4. The process according to claim 1 in which 25 the solution of condensation product employed is a water solution to which a thickening agent has been added.

5. The process of joining wooden surfaces which comprises applying to said surfaces a solution'of 30 a water soluble condensation product of .a urea and formaldehyde to which condensation product an acid reacting agent inert to formaldehyde has been added shortly before the solution applying pressing the surfaces to- 35- the surfaces together 'gether. KARL VIERLING.

MA'IIHIAS SCHMIHING. HUGO KLINGENBERG.

parallel direction of the fibres in the single slabs, 5 

